1. Field of the Invention
The present invention relates to metallic materials useful as highly active catalysts by which used spent chlorofluorocarbons (hereinafter referred to as "flons") can be easily decomposed to carbon dioxide, hydrofluoric acid and hydrochloric acid for purification or reuse thereof and which can retain their high activity, even if hydrofluoric acid and hydrochloric acid, which attack metallic materials, are produced by decomposition of the flons.
2. Description of the Prior Art
Since flons destroy ozonosphere, spent flons must be decomposed for purification. Decomposition of flons has heretofore been attempted by several methods, for example, by mixing flons with a large amount of methane to cause combustion, by the reaction of flons with water under high-temperature and high-pressure conditions, by the reaction of flons with water using zeolite as a catalyst, etc.
The present Inventors have conducted detailed studies and directed their attention to amorphous alloys which can contain large amounts of various elements having different properties. As a result, various kinds of amorphous alloys having properties desirable as catalysts for electrodes have been found. Based on the inventors' previous studies on such amorphous alloy catalysts for electrodes, two of the present inventors have further investigated catalysts for production of hydrofluoric acid, hydrochloric acid and carbon dioxide by the reaction of flons with water at low temperatures and found that highly active catalysts can be obtained from certain amorphous alloys, as shown in Japanese Patent Application No. 2-45661. The Japanese Patent Application is directed to the following three aspects:
1. Amorphous alloy catalysts for decomposition of flons characterized by being immersed in hydrofluoric acids for activation and consisting of 20 to 70 at % of at least one element selected from the group consisting of Nb and Ta, 0.5 to 20 at % of at least one element selected from the group consisting of Ru, Rh, Pd, Pt, and Ir, and the substantial balance being at least one element selected from the group consisting of Ni and Co.
2. Amorphous alloy catalysts for decomposition of flons characterized by being immersed in hydrofluoric acids for activation and consisting of 20 to 80 at % of at least one element selected from the group consisting of Ti and Zr, 0.5 to 20 at % of at least one element selected from the group consisting or Ru, Rh, Pd, Pt and Ir, and the substantial balance being 10 at % or more of at least one element selected from the group consisting of Ni and Co.
3 Amorphous alloy catalysts for decomposition of flons characterized by being immersed in hydrofluoric acids for activation and consisting of 20 to 80 at % in total of at least one element selected from the group consisting of Ti and Zr and at most 70 at % of at least one element selected from the group consisting of Nb and Ta, 0.5 to 20 at % of at least one element selected from the group consisting of Ru, Rh, Pd, Pt and Ir, and the substantial balance being 10 at % or more of at least one element selected from the group consisting of Ni and Co.
Since the reaction of flons with oxygen is an endothermic reaction, flons should be mixed with a large amount of methane for decomposition thereof by combustion. Therefore, this decomposition process is impractical. On the other hand, in the direct reaction of flons with water, the reaction must be carried out under the conditions of high-temperature and high-pressure. In order to decompose flons with a reduced consumption of energy, the reaction of flons with water should be carried out at low temperatures, using a catalyst. However, catalysts exhibiting superior performance in the reaction have not been found. Since the decomposition of flons by the reaction with water produces hydrofluoric acid and hydrochloric acid, besides carbon dioxide, metallic catalysts used for the decomposition are readily deactivated due to attack by these halogen acids.
Therefore, catalysts having a high activity and a high resistance against the foregoing halogen acids have been strongly demanded.